1. Field of the Invention
The present invention relates to a frequency hopping sequence generator and, more particularly, to a frequency hopping sequence generator using a single binary sequence generator adopted for a multi-group frequency hopping frequency division multiple access (FH-FDMA) communication system
2. Description of the Background Art
The multi-group FH-FDMA is a frequency-hopping spread spectrum (FHSS) communication system exerting an excellent performance in a threatening environment such as jamming, wire-tapping, frequency selection fading, a position detection or the like.
The characteristics of the frequency hopping sequence generator required for the multi-group FH-FDMA communication system are facilitation of a key management, auto-correlation of frequency hopping sequence assigned to each group, and orthogonality (non-collision of chip) between groups or independence.
Let q denote the number of frequency slots in a FHSS system and let fi denote the center frequency of the i-th slot, 0≦i≦q−1. The center frequencies are usually chosen that the slots be spaced uniformly across the frequency band allotted to the system. A FH pattern is a sequence x=(x0, x1, . . . , XN−1) of N elements from the set f0, fi, . . . , fq−1 specifying the order in which the slots are to be used by a particular transmitter. However, it is not necessary that the elements of the set be the center frequencies of the slots. All the various properties of hopping patterns can be described provided only that the set contains q distinct elements. In short, one can also regard a hopping pattern as a sequence of elements, and the pattern can always be transformed into a sequences of frequencies by a suitable one to one mapping from this set to f0, fi, . . . , fq−1. This is the viewpoint that will be taken in the rest of this document. In particular, hopping patterns will be viewed as sequences of elements from the finite field q=2k.
In general, the frequency hopping sequence generator used in the FHSS system uses a non-binary sequence converter that maps binary outputs of a binary m-sequence generator into non-binary sequences, i.e. sequences of elements aforementioned.
FIG. 1 is a schematic block diagram of a frequency hopping sequence generator consisting of a binary sequence generator 100 and a non-binary sequence converter 200 in accordance with a conventional art.
With reference to FIG. 1, the frequency hopping sequence is generated by the non-binary sequence converter 200 which, as mentioned above, maps the consecutive binary outputs of the general binary sequence generator 100 into the non-binary sequences.
Since a periodic binary m-sequence of span-n characteristics generates different 2n tuples for one period when observing consecutive n tuples, when read out k (k<n) tuples of the binary sequence continuously, the occurrence frequency of each of 2k tuples becomes 2n−k. In this manner, consecutive k tuples of the binary sequence generator 100 can be simply converted into frequency hopping sequences having 2k symbols with an even occurrence frequency.
FIG. 2 shows an internal construction of the non-binary sequence converter 200 of FIG. 1, illustrating that a binary sequence is mapped into a non-binary sequence when the number of frequency hopping slots is an exponent of 2.
With reference to FIG. 2, an exclusive-OR operator 230 exclusive-ORs outputs of a shift register 210 and corresponding outputs of an offset data storing unit 220 to generate a non-binary sequence (Y1, Y2, . . . , Yv). A set of different sequences generated according to values stored in the offset data storing unit 220 can be used as a sequence set for a FH-CDMA.
However, when the conventional frequency hopping sequence generator is applied to the multi-group FH-FDMA communication system, the number of the frequency hopping sequence generator as shown in FIG. 1 is required as many as groups, resulting in hardware complexity of the communication system. Also, since the number of keys is required as many as groups, the keys should be managed as many as the groups, resulting in degraded facilitation of key management.
In addition, problems relating to the synchronization and orthogonality (chip non-collision) or independence between frequency hopping sequence generators should be solved.